The formation of a cataract in a human eye not only causes gradual loss of vision and eventual total blindness but, if allowed to progress to hypermaturity, may cause total degeneration of the eye. Restoring vision to an eye in which a cataract has formed involves completely removing the lens. This is an exceedingly delicate operation and requires a subsequent substantial immobility of the patient for approximately 3 weeks. Because of the relatively large incision made in the eye and the sutures required, any sudden or erratic movement within weeks after the operation may cause the eye to be irreparably damaged.
Accordingly, numerous instruments have been designed to be inserted into the eye through a small puncture to remove lens material or other materials such as blood clot, vitreous opacities, adhesions, and the like. A small puncture requires only one or two sutures, thereby requiring less immobilization time on the part of the patient.
Some instruments utilize vibrating chisel-shaped or pointed members. Some others provide treatment fluid under controlled pressure to the operative site and also provide suction to remove macerated material from the site. Complicated controls such as computers are required when suction is applied to the eye to prevent sudden increases in the suction as, for example, when macerated material blocking the suction passage suddenly breaks loose.
An instrument such as that shown in U.S. Pat. No. 3,736,938 utilizes a combination of an ultrasonically vibrating tube with a rotating cutter bit which has spiral grooves to evacuate macerated material along with used treatment fluid. Many opthamologists, however, are concerned that using ultrasonic energy in the eye may cause damage as yet unknown.
A number of problems occur with regard to rotating a cutting member at high speed where the necessary removal of macerated material is to be accomplished without applying suction to the eye. Some of these problems include heating, loose tolerances required to reduce heating and its effects, and binding of the rotating cutter because of thickening and hardening of the macerated material as it is pumped out of the eye. Of course, the faster the cutter rotates, the more acute these problems become.
It has been found that some tissue, such as a hard cataract, is very difficult to macerate with a surgical tool of the type using a rotating cutter. This appears to occur because the cataract moves from the force from the cutter which is attempting to cut the hard material.